1. Field of the Invention
The present invention relates to lens driving devices that are generally used for cameras such as cameras mounted on cellular phones. More particularly, the present invention relates to the technology to drive, position and retain a lens or a lens unit in an optical axial direction.
2. Related Background Art
A camera device that is mounted on a cellular phone (i.e., portable telephone) with camera typically uses a driving system that drives a lens between two positions, an ordinary photographing position where an ordinary photographing takes place, and a close-up photographing position where the lens is positioned slightly closer to subject by a predetermined distance than its position in the ordinary photographing. However, it would not be practical, from a size point of view, to mount a lens driving device equipped with a motor on equipment such as cellular phones with camera. For this reason, lens driving devices of the type which directly, magnetically drives a lens is mounted on cellular phones with camera.
A lens driving device of a magnetic drive type is typically equipped with a cylindrical case that retains a lens, a ring-shaped drive magnet mounted on an outer circumference of the case, and a driving coil that opposes the driving magnet. Energization of the driving coil is controlled to magnetically drive the cylindrical case that retains the lens in an optical axis direction to a desired position, and the cylindrical case is magnetically retained at the desired position.
Also, another lens driving device may be equipped with a case having a lens mounted thereon, wherein the case is rotated in its circumferential direction by the driving device such that the case is moved in an optical axis direction.
However, in the former type, namely, the lens driving device in which the case that retains the lens is magnetically driven in an optical axis direction to a desired position and the case is magnetically retained at the position, if the lens is to be retained at the position for a long period of time, the driving coil needs to be energized during that period. For this reason, the lens driving device of the former type has a problem, namely, it consumes a large amount of power, and therefore is not suitable for mounting on cellular phones with camera.
In contrast, in the latter type, namely, the lens driving device in which the case is rotated in its circumferential direction to move the case in a rotational axis direction (i.e., optical axis direction), there is an advantage that the lens driving device has a relatively low power consumption. However, the lens driving device of the latter type has a complex structure and includes a large number of components, and therefore is not suitable for mounting on cellular phones with camera.